Noise emitted by a tire rolling across a road surface is attributable mainly to the vibrations of the contacting surface of the tire with road surface irregularities that generate various acoustic waves. At least a portion of these acoustic waves can be perceived by the human ear as noise both inside and outside of the vehicle. The amplitude of the noise is dependent on e.g., vibration modes of the tire and also the nature of the road surface on which the vehicle moves. The frequency range corresponding to the noise generated by the tire typically ranges from about 20 Hz to 4000 Hz.
Noise outside the vehicle can be attributed to various interactions between e.g., the tire and the road surface and the tire and the air, each of which can cause discomfort to persons along the moving vehicle. The sources of such noise include the impact of the roughness of the road with the contact area of the tire as well as noise generated due to the arrangement of the elements of the tread and its resonance along different paths. The frequency range for such noise can range from about 300 Hz to about 3000 Hz.
Regarding the noise heard inside the vehicle, the modes of sound propagation include vibrations transmitted through the wheel center and the suspension system (up to about 400 Hz) as well as vibrations from aerial transmission of acoustic waves, which can include the high frequency spectrum (about 600 Hz and over).
One important contribution to the noise heard inside the vehicle is provided by cavity noise, which refers to the discomfort caused by the resonance of the air within the tire cavity. This cavity noise is predominant in a specific frequency spectrum between 200 Hz and 250 Hz depending on the geometry of the tire.
To reduce the rolling noise of a tire, particularly cavity noise, it is known to provide the inner wall of the tire with a layer of foam such as e.g., a foam as described in patents or patent applications WO 2006/117944 or U.S. Pat. No. 7,975,740, WO 2007/058311 and U.S. 2009/0053492, U.S. 2007/0175559, WO 2008/062673 and U.S. 2010/0038005, U.S. 2009/0053492, WO 2010/000789 and U.S. 2011/0308677, EP 1529665 or U.S. Pat. No. 7,182,114.
Challenges exist with development of processes and equipment for repeatedly locating the foam in the tire cavity and along the interior surface or wall. For example, tires are currently produced in a wide range of sizes and shapes requiring either different placement machines or adjustability of such machines. Also, if the foam is to be placed by insertion in the tire cavity against the inner surface of the tire in the crown portion, navigation past the tire seat must be considered. The tire seat has a smaller diameter relative to the diameter of the inner surface of the tire. Other challenges also exist.
Accordingly, a system for positioning noise attenuating foam inside a tire against the interior surface would be useful. Such a system that can consistently position the foam over a range of different tires sizes and shapes would be beneficial. Such a system that can be automated would also be particularly useful.